Visual quantitative measurement system and method for reverse thrust cascade outlet airflow angle

Abstract

The invention discloses a visual quantitative measurement system and method for an air flow angle at an outlet of a reverse thrust cascade, and belongs to the field of pneumatic technologies of engines. The device comprises a binocular photogrammetry system, a digital pulse delay signal generator, a computer, a square guide rail and a wrench sliding block, the binocular photogrammetry system is installed on the square guide rail in a sliding mode through the wrench sliding block, and the binocular photogrammetry system is connected with the digital pulse delay signal generator. An image acquired by the binocular photogrammetry system is input into the computer for storage, and the digital pulse delay signal generator is connected with the computer. In order to overcome the problem that the existing silk thread technology can only display visually and qualitatively, the quantitative measurement capability of the airflow angle at the outlet of the reverse thrust cascade of the whole machine of the reverse thrust full-ring performance test piece ground table is realized.

Description

Technical Field

[0001] The invention relates to an airflow angle measurement method, in particular to a visual quantitative measurement system and method for the airflow angle of a thrust reverser cascade outlet, belonging to the field of engine aerodynamic technology. Background Art

[0002] Modern aircraft engines widely use cascade thrust reversers for braking. This device has a compact structure, high reliability, and stable reverse thrust. It can well control the reverse thrust airflow and obtain a higher reverse thrust efficiency. The effective area ratio and reverse thrust efficiency when the reverse thrust is fully opened are important indicators in the reverse thrust design requirements, which determine the matching with the engine during the use of the reverse thrust and the reverse thrust provided to the aircraft. Due to the lack of experience in reverse thrust design in China, it is not enough to support the accuracy of CFD numerical simulation methods in reverse thrust performance simulation. Therefore, it is necessary to carry out reverse thrust reduction ratio full-ring performance tests to verify and optimize the reverse thrust aerodynamic design and provide technical reserves for reverse thrust aerodynamic design. The cascade density and outlet airflow angle are directly related to the axial reverse thrust coefficient and the flow coefficient, and have a great influence on the reverse thrust performance. Therefore, measuring the outlet airflow direction of cascades with different densities when the reverse thrust is fully opened is an important part of the test.

[0003] Thread is a tracing method for observing flow patterns. By sticking the thread on the surface of the model, the direction of the airflow can be determined by the movement of the thread. However, the traditional thread method is only an intuitive qualitative display, which cannot meet the analysis requirements of the influence of the actual airflow deflection angle on the reverse thrust performance of the cascade. Therefore, it is urgent to develop a visual quantitative measurement method for the airflow angle at the outlet of the reverse thrust cascade, so as to accurately and quantitatively obtain the circumferential angle and axial angle of the airflow at the outlet of the cascade, and solve the measurement and analysis requirements of the reverse thrust full-ring performance test. Summary of the invention

[0004] In order to overcome the problem that the existing wire technology can only intuitively and qualitatively display, the present invention realizes the quantitative measurement capability of the reverse thrust cascade outlet airflow angle of the reverse thrust full ring performance test piece ground platform, and provides a visual quantitative measurement system and method for the reverse thrust cascade outlet airflow angle. A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to determine the key or important parts of the present invention, nor is it intended to limit the scope of the present invention.

[0005] The technical solution of the present invention:

[0006] Solution 1: A visual quantitative measurement system for the airflow angle at the outlet of a thrust reverser blade cascade, comprising a binocular photogrammetry system, a digital pulse delay signal generator, a computer, a square guide rail, and a wrench slider. The binocular photogrammetry system is slidably installed on the square guide rail through the wrench slider, the binocular photogrammetry system is connected to the digital pulse delay signal generator, the images collected by the binocular photogrammetry system are input into the computer for storage, and the digital pulse delay signal generator is connected to the computer.

[0007] Preferably, the binocular photogrammetry system comprises a first imaging device and a second imaging device, and there is a baseline distance between the first imaging device and the second imaging device.

[0008] Preferably, the first imaging device and the second imaging device are both fixedly connected to the square guide rail via a wrench slider.

[0009] Preferably: the first imaging device comprises a first camera, a first lens, a first filter, a first annular light source, a first fixing ring, a first fixing plate and a first connecting bracket, the first filter is connected to the first lens through a thread, the first lens is connected to the first camera through a thread or a bayonet, the first camera is fixedly mounted on the first fixing plate, the first annular light source is placed on the first fixing ring, and is connected to the first fixing plate through the connecting bracket;

[0010] The second imaging device includes a second camera, a second lens, a second filter, a second annular light source, a second fixing ring, a second fixing plate and a second connecting bracket. The second filter is connected to the second lens via a thread, the second lens is connected to the second camera via a thread or a bayonet, the second camera is fixedly mounted on the second fixing plate, and the second annular light source is placed on the second fixing ring and connected to the second fixing plate via a second connecting bracket.

[0011] Solution 2: A visual quantitative measurement method for the airflow angle at the outlet of a thrust reverser cascade, which is implemented based on a visual quantitative measurement system for the airflow angle at the outlet of a thrust reverser cascade described in Solution 1, and includes the following steps:

[0012] Step 1, thread pasting: paste the thread at the circumferential center of the grid at the trailing edge of the flow direction blade of the cascade block along the flow direction of the cascade block to be measured, and then install the cascade block on the support ring of the reverse thrust full ring performance test piece;

[0013] Step 2, arrangement and calibration of binocular photogrammetry system: arrange the binocular photogrammetry system on the outer side of the cascade block after the thread is pasted in step 1, align the first imaging device and the second imaging device of the binocular photogrammetry system with the cascade grille to be measured, so that the cascade grille of the cascade block is within the camera field of view; adjust the focal length of the first lens and the second lens to make the cascade image clear, and adjust the first ring light source and the second ring light source for fill light according to the site conditions; before the test, use the checkerboard calibration plate to calibrate the camera parameters of the binocular photogrammetry system; during the test, ensure that there is no relative displacement between the first imaging device and the second imaging device in the binocular photogrammetry system;

[0014] Step 3, grid coordinate system calibration: before the test, increase the exposure time of the first camera and the second camera, collect images, define the origin of the grid coordinates in the cascade block as (m,n), which is surrounded by the corner points (m,n), (m+1,n), (m,n+1) and (m+1,n+1), define the axis of the model coordinate system along the airflow direction as the positive direction of the x-axis, the direction of the axis perpendicular to the cascade block plane is the opposite direction of the z-axis, and the y-axis satisfies the right-hand rule, that is, the positive direction of x points to (m,n+1), and the positive direction of y points to (m+1,n), reconstruct the spatial three-dimensional coordinates of the corner points (m,n), (m+1,n), and (m,n+1) in the camera coordinate system, and calculate the axis vector of the current cascade block grid and According to the right-hand rule, we get Then obtain the grid coordinate system vector matrix;

[0015] Step 4, test image acquisition: reduce the exposure time to ensure that there is no motion blur in the image when the silk thread moves; after the drop pressure ratio is judged to be stable, control the first camera and the second camera to perform synchronous acquisition to obtain the silk thread image during the test process

[0016] Step 5, 3D reconstruction of the endpoints of the silk thread: Based on the line detection technology, the image coordinates of the silk thread are obtained respectively, and the silk thread targets are matched with the same name through the corresponding constraints. After matching, the image coordinates of the two end points of the silk thread in the grid (m, n) are extracted, and the 3D coordinates of the endpoints of the silk thread in the camera coordinate system are reconstructed by triangulation;

[0017] Step 6, calculation of outlet airflow angle: define the airflow circumferential angle θ as the angle between the projection of the wire segment vector on the grid yoz plane and the y-axis, and the airflow axial angle φ as the angle between the wire segment vector and the x-axis. According to the line endpoint coordinates obtained in step 5 and the grid coordinate system vector matrix obtained in step 3, the outlet airflow angle represented by the wire at the current position is obtained.

[0018] Preferably, in step 1, the length of the thread pasted at the circumferential center of the grid at the trailing edge of the flow blade of the cascade block along the flow direction of the cascade block should not exceed the blade spacing, that is, the distance between corresponding points of two adjacent flow blades along the frontal line.

[0019] Preferably: in step 3: before the test, a clear cascade image I is captured by increasing the exposure time. 1 , I 2 , to I 1 , I 2 Perform image processing and obtain the image coordinates of the three corner points at the grid positions (m,n), (m+1,n), and (m,n+1) by extracting the corner points and and Based on the triangulation method, the spatial three-dimensional coordinates P of these three corner points in the camera coordinate system are obtained. m,n , P m+1,n and P m,n+1 , where P m,n and P m+1,n Circumferentially adjacent, P m,n and P m,n+1 Flow to adjacent areas;

[0020] Calculate the axis vector of the coordinate system of the current grid:

[0021]

[0022]

[0023]

[0024] The coordinate system vector matrix of the cascade block grid is obtained

[0025] Preferably: in step 5: based on the Steger line center detection algorithm, the two camera images of the wire in the system are obtained respectively. The line center image coordinates l 1 and l 2 After matching the thread targets with the same name according to the corresponding constraints, the image coordinates of the two end points of the thread in the grid (m,n) are extracted. and The spatial three-dimensional coordinates L of the two end points of the silk thread in the camera coordinate system are obtained based on triangulation reconstruction. mn,1 and L mn,2 , where L mn,1 is the end point of the thread, L mn,2 It is the free end point of the wire.

[0026] Preferably, in the steps: the three-dimensional coordinates of the end points of the thread in the camera coordinate system are rotated by the relationship R mn Convert to the grid coordinate system to get the new thread endpoint coordinate E mn,1 =L mn,1 / R mn and E mn,2 =L mn,2 / R mn , then in the grid coordinate system, the thread vector under the action of airflow during the test is That is, the outlet airflow angle represented by the silk line at the current position is obtained;

[0027] The angle between the projection of this vector on the grid yoz plane and the y-axis:

[0028]

[0029] The angle between the projection of this vector on the grid xoy plane and the x-axis:

[0030]

[0031] The present invention has the following beneficial effects:

[0032] 1. The present invention does not require special optical path construction and modification. By detecting the center of the silk line in the image, extracting the end points of the line segment for three-dimensional reconstruction and post-processing solution, the circumferential angle and axial angle of the airflow at the cascade outlet can be obtained, which reduces the complexity of the experimental equipment, reduces errors and manual intervention, improves measurement accuracy, enhances operational flexibility, and improves measurement efficiency.

[0033] 2. The present invention realizes the quantitative measurement of the airflow angle at the outlet of the whole reverse thrust cascade on the ground platform, solves the measurement and analysis requirements of the reverse thrust full-ring performance test, can efficiently and accurately measure the circumferential angle and axial angle of the airflow at the outlet of the cascade, and optimizes the experimental process and result quality of the airflow angle measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of a visual quantitative measurement method for inferring the airflow angle at the cascade outlet;

[0035] Figure 2 Schematic diagram of the structure of the cascade block in the present invention, wherein (a) is a diagram indicating the circumferential center position of the cascade block, and (b) is a schematic diagram of the cascade coordinate system;

[0036] Figure 3 It is a structural schematic diagram of the binocular photogrammetry system of the present invention;

[0037] Figure 4 is a schematic structural diagram of a first imaging device and a second imaging device of the present invention;

[0038] In the figure, 1-binocular photogrammetry system, 2-digital pulse delay signal generator, 3-computer, 4-square guide rail, 5-wrench slider, 6-blade block, 7-flow blade trailing edge, 8-grid circumferential center position, 11-first imaging device, 12-second imaging device, 111-first camera, 112-first lens, 113-first filter, 114-first annular light source, 115-first fixing ring, 116-first fixing plate, 117-first connecting bracket, 121-second camera, 122-second lens, 123-second filter, 124-second annular light source, 125-second fixing ring, 126-second fixing plate, 127-second connecting bracket. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0040] Specific implementation method 1: Combination Figure 1-Figure 4 The present embodiment is described. The present embodiment is a visual quantitative measurement system for the airflow angle of the reverse thrust cascade outlet, comprising a binocular photogrammetry system 1, a digital pulse delay signal generator 2, a computer 3, a square guide rail 4, and a wrench slider 5. The binocular photogrammetry system 1 is slidably installed on the square guide rail 4 through the wrench slider 5. The binocular photogrammetry system 1 is connected to the digital pulse delay signal generator 2. The image collected by the binocular photogrammetry system 1 is input into the computer 3 for storage. The digital pulse delay signal generator 2 is connected to the computer 3. The computer 3 is used to input a working signal to the digital pulse delay signal generator 2.

[0041] The binocular photogrammetry system 1 includes a first imaging device 11 and a second imaging device 12 . The first imaging device 11 and the second imaging device 12 have the same structure and have a baseline distance.

[0042] The digital pulse delay signal generator 2 is used to give an external trigger signal to the first imaging device 11 and the second imaging device 12 to perform image acquisition, so as to ensure synchronous image acquisition of the first imaging device 11 and the second imaging device 12;

[0043] The first imaging device 11 and the second imaging device 12 are both fixedly connected to the square guide rail 4 via the wrench slider 5 .

[0044] The first imaging device 11 includes a first camera 111, a first lens 112, a first filter 113, a first annular light source 114, a first fixing ring 115, a first fixing plate 116 and a first connecting bracket 117. The first filter 113 is connected to the first lens 112 via a thread, the first lens 112 is connected to the first camera 111 via a thread or a bayonet, the first camera 111 is fixedly mounted on the first fixing plate 116, and the first annular light source 114 is placed on the first fixing ring 115 and connected to the first fixing plate 116 via a connecting bracket 117.

[0045] The second imaging device 12 includes a second camera 121, a second lens 122, a second filter 123, a second annular light source 124, a second fixing ring 125, a second fixing plate 126 and a second connecting bracket 127. The second filter 123 is connected to the second lens 122 via a thread, the second lens 122 is connected to the second camera 121 via a thread or a bayonet, the second camera 121 is fixedly mounted on the second fixing plate 126, the second annular light source 124 is placed on the second fixing ring 125, and is connected to the second fixing plate 126 via a second connecting bracket 127.

[0046] The first ring light source 114 provides additional lighting for the first ring camera 111, and similarly, the second ring light source 124 provides additional lighting for the second camera 121; taking the first ring light source 114 and the first ring camera 111 as an example, since the first ring light source 114 directly surrounds the front of the first ring lens 112, the light can be evenly irradiated onto the silk thread in the same direction, which helps to reduce shadows and light spots, make the silk thread details clearer, and improve image quality.

[0047] Specific implementation method 2: Combination Figure 3-Figure 4 This embodiment is described. A visual quantitative measurement method for the outlet airflow angle of a reverse thrust cascade in this embodiment is implemented based on a visual quantitative measurement system for the outlet airflow angle of a reverse thrust cascade described in the first embodiment, and includes the following steps:

[0048] Step 1, thread pasting: paste the thread at the grid circumferential center position 8 of the flow direction blade trailing edge 7 of the cascade block 6 along the flow direction of the cascade block 6 to be measured, and then install the cascade block 6 on the support ring of the reverse thrust full ring performance test piece;

[0049] Step 2, arrangement and calibration of the binocular photogrammetry system 1: arrange the binocular photogrammetry system 1 on the outer side of the cascade block 6 after the thread is pasted in step 1, and align the first imaging device 11 and the second imaging device 12 of the binocular photogrammetry system 1 with the cascade grille to be measured, so that the cascade grille of the cascade block 6 is located in the camera field of view; adjust the focal length of the first lens 112 and the second lens 122 to make the cascade image clear, and adjust the first ring light source 114 and the second ring light source 124 for fill light according to the site conditions; before the test, use the checkerboard calibration plate to calibrate the camera parameters of the binocular photogrammetry system 1; during the test, ensure that there is no relative displacement between the first imaging device 11 and the second imaging device 12 in the binocular photogrammetry system 1;

[0050] Step 3, grid coordinate system calibration: before the test, increase the exposure time of the first camera 111 and the second camera 121, collect images, define the origin of the grid coordinates in the blade block 6 as (m, n), which is surrounded by the corner points (m, n), (m+1, n), (m, n+1) and (m+1, n+1), define the axis of the model coordinate system along the airflow direction as the positive direction of the x-axis, the plane perpendicular to the blade block 6 points to the axis direction as the opposite direction of the z-axis, and the y-axis satisfies the right-hand rule, that is, the positive direction of x points to (m, n+1), and the positive direction of y points to (m+1, n), reconstruct the spatial three-dimensional coordinates of the corner points (m, n), (m+1, n), (m, n+1) in the camera coordinate system, and calculate the axis vector of the current blade block 6 grid and According to the right-hand rule, we get Then obtain the grid coordinate system vector matrix;

[0051] Step 4, test image acquisition: reduce the exposure time to ensure that the image is free of motion blur when the silk thread moves; after the pressure drop ratio is determined to be stable, the first camera 111 and the second camera 121 in the control system are synchronously acquired to obtain the silk thread image during the test process.

[0052] Step 5, 3D reconstruction of the endpoints of the silk thread: Based on the line detection technology, the image coordinates of the silk thread are obtained respectively, and the silk thread targets are matched with the same name through the corresponding constraints. After matching, the image coordinates of the two end points of the silk thread in the grid (m, n) are extracted, and the 3D coordinates of the endpoints of the silk thread in the camera coordinate system are reconstructed by triangulation;

[0053] Step 6, calculation of outlet airflow angle: define the airflow circumferential angle θ as the angle between the projection of the wire segment vector on the grid yoz plane and the y-axis, and the airflow axial angle φ as the angle between the wire segment vector and the x-axis. According to the line endpoint coordinates obtained in step 5 and the grid coordinate system vector matrix obtained in step 3, the outlet airflow angle represented by the wire at the current position is obtained.

[0054] In step 1: along the flow direction of the cascade block 6, the length of the thread pasted at the grid circumferential center position 8 of the trailing edge 7 of the flow blade of the cascade block 6 should not exceed the blade pitch, that is, the distance between the corresponding points of two adjacent flow blades along the frontal line direction, so as to ensure that the thread only indicates the outlet airflow direction of the cascade as much as possible, and avoid the occurrence of swing or even reversal due to excessive length of the thread. Then install the cascade block 6 on the support ring of the reverse thrust full ring performance test piece at the specified position.

[0055] In step 2: the binocular photogrammetry system 1 is arranged to avoid the airflow direction, and each binocular photogrammetry system 1 has a first camera 111 and a second camera 121, and the common field of view of the binocular photogrammetry system 1 is aligned with the grid of the cascade block 6 to be measured. Select the first lens 112 and the second lens 122 with appropriate focal lengths, adjust the focal length and aperture so that the field of view meets the measurement requirements, and fill in the light appropriately according to the on-site conditions. One binocular photogrammetry system 1 can meet the measurement requirements of one quadrant of the test piece. If a full-ring test is required, four binocular photogrammetry systems 1 need to be arranged.

[0056] In step 3: before the test, a clear cascade image is captured by increasing the exposure time. 1 , I 2 , to I 1 , I 2 Perform image processing and obtain the image coordinates of the three corner points at the grid positions (m,n), (m+1,n), and (m,n+1) by extracting the corner points and and Based on the triangulation method, the spatial three-dimensional coordinates P of these three corner points in the camera coordinate system are obtained. m,n , P m+1,n and P m,n+1 , where P m,n and P m+1,n Circumferentially adjacent, P m,n and P m,n+1 Flow to adjacent areas;

[0057] Calculate the axis vector of the coordinate system of the current grid:

[0058]

[0059]

[0060]

[0061] The coordinate system vector matrix of the grid of the blade block 6 is obtained

[0062] In step 5: based on the Steger line center detection algorithm, the two camera images of the wire in the system are obtained respectively. The line center image coordinates l 1 and l 2 After matching the thread targets with the same name according to the corresponding constraints, the image coordinates of the two end points of the thread in the grid (m,n) are extracted. and The spatial three-dimensional coordinates L of the two end points of the silk thread in the camera coordinate system are obtained based on triangulation reconstruction. mn,1 and L mn,2 , where L mn,1 is the end point of the thread, L mn,2 It is the free end point of the wire.

[0063] In the steps: the three-dimensional coordinates of the endpoints of the thread in the camera coordinate system are rotated by the rotation relationship R mn Convert to the grid coordinate system to get the new thread endpoint coordinate E mn,1 =L mn,1 / R mn and E mn,2 =L mn,2 / R mn , then in the grid coordinate system, the thread vector under the action of airflow during the test is That is, the outlet airflow angle represented by the silk line at the current position is obtained;

[0064] The angle between the projection of this vector on the grid yoz plane and the y-axis:

[0065]

[0066] The angle between the projection of this vector on the grid xoy plane and the x-axis:

[0067]

[0068] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be arranged and combined, and those skilled in the art can exhaust all possibilities based on the mathematical knowledge of arrangement and combination. Therefore, the present invention will no longer describe the technical solutions after arrangement and combination one by one, but it should be understood that the technical solutions after arrangement and combination have been disclosed by the present invention.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A visual quantitative measurement system for the airflow angle of the reverse thrust cascade outlet, characterized in that: The invention comprises a binocular photogrammetry system (1), a digital pulse delay signal generator (2), a computer (3), a square guide rail (4), and a spanner slider (5); the binocular photogrammetry system (1) is slidably mounted on the square guide rail (4) via the spanner slider (5); the binocular photogrammetry system (1) is connected to the digital pulse delay signal generator (2); images collected by the binocular photogrammetry system (1) are input into the computer (3) for storage; and the digital pulse delay signal generator (2) is connected to the computer (3).

2. A visual quantitative measurement system for the thrust reverser blade outlet airflow angle according to claim 1, characterized in that: The binocular photogrammetry system (1) comprises a first imaging device (11) and a second imaging device (12), wherein a baseline distance exists between the first imaging device (11) and the second imaging device (12).

3. A visual quantitative measurement system for the thrust reverser blade outlet airflow angle according to claim 2, characterized in that: The first imaging device (11) and the second imaging device (12) are both fixedly connected to the square guide rail (4) via a spanner slider (5).

4. A visual quantitative measurement system for the thrust reverser blade outlet airflow angle according to claim 3, characterized in that: The first imaging device (11) comprises a first camera (111), a first lens (112), a first filter (113), a first annular light source (114), a first fixing ring (115), a first fixing plate (116) and a first connecting bracket (117); the first filter (113) is connected to the first lens (112) via a thread; the first lens (112) is connected to the first camera (111) via a thread or a bayonet; the first camera (111) is fixedly mounted on the first fixing plate (116); the first annular light source (114) is arranged on the first fixing ring (115) and connected to the first fixing plate (116) via a connecting bracket (117); The second imaging device (12) comprises a second camera (121), a second lens (122), a second filter (123), a second annular light source (124), a second fixing ring (125), a second fixing plate (126) and a second connecting bracket (127); the second filter (123) is connected to the second lens (122) via a thread; the second lens (122) is connected to the second camera (121) via a thread or a bayonet; the second camera (121) is fixedly mounted on the second fixing plate (126); the second annular light source (124) is placed on the second fixing ring (125) and connected to the second fixing plate (126) via a second connecting bracket (127).

5. A visual quantitative measurement method for the outlet airflow angle of a thrust reverser cascade, which is implemented by relying on the visual quantitative measurement system for the outlet airflow angle of a thrust reverser cascade according to claim 4, characterized in that: The following steps are involved: Step 1, thread pasting: paste the thread at the grid circumferential center position (8) of the trailing edge (7) of the flow direction blade of the cascade block (6) along the flow direction of the cascade block (6) to be measured, and then install the cascade block (6) on the support ring of the reverse thrust full ring performance test piece; Step 2, arrangement and calibration of the binocular photogrammetry system (1): the binocular photogrammetry system (1) is arranged on the outer side of the cascade block (6) after the thread is pasted in step 1, and the first imaging device (11) and the second imaging device (12) of the binocular photogrammetry system (1) are aligned with the cascade grille to be measured, so that the cascade grille of the cascade block (6) is located within the camera field of view; the focal lengths of the first lens (112) and the second lens (122) are adjusted to make the cascade image clear, and the first annular light source (114) and the second annular light source (124) are adjusted according to the on-site conditions to provide fill light; before the test, the camera parameters of the binocular photogrammetry system (1) are calibrated using a checkerboard calibration plate; during the test, it is ensured that there is no relative displacement between the first imaging device (11) and the second imaging device (12) in the binocular photogrammetry system (1); Step 3, grid coordinate system calibration: before the test, increase the exposure time of the first camera (111) and the second camera (121), collect images, define the origin of the grid coordinates in the cascade block (6) as (m, n), which is surrounded by the corner points (m, n), (m+1, n), (m, n+1) and (m+1, n+1), define the axis of the model coordinate system along the airflow direction as the positive direction of the x-axis, the plane perpendicular to the cascade block (6) points to the axis direction as the opposite direction of the z-axis, and the y-axis satisfies the right-hand rule, that is, the positive x direction points to (m, n+1), and the positive y direction points to (m+1, n), reconstruct the spatial three-dimensional coordinates of the corner points (m, n), (m+1, n), and (m, n+1) in the camera coordinate system, and calculate the axis vector of the current cascade block (6) grid and According to the right-hand rule, we get Then obtain the grid coordinate system vector matrix; Step 4, test image acquisition: reduce the exposure time to ensure that the image is free of motion blur when the silk thread moves; after the drop pressure ratio is determined to be stable, control the first camera (111) and the second camera (121) to perform synchronous acquisition to obtain the silk thread image during the test process Step 5, 3D reconstruction of the endpoints of the silk thread: Based on the line detection technology, the image coordinates of the silk thread are obtained respectively, and the silk thread targets are matched with the same name through the corresponding constraints. After matching, the image coordinates of the two end points of the silk thread in the grid (m, n) are extracted, and the 3D coordinates of the endpoints of the silk thread in the camera coordinate system are reconstructed by triangulation; Step 6, calculation of outlet airflow angle: define the airflow circumferential angle θ as the angle between the projection of the wire segment vector on the grid yoz plane and the y-axis, and the airflow axial angle φ as the angle between the wire segment vector and the x-axis. According to the line endpoint coordinates obtained in step 5 and the grid coordinate system vector matrix obtained in step 3, the outlet airflow angle represented by the wire at the current position is obtained.

6. A visual quantitative measurement method for the airflow angle at the outlet of the thrust reverser blade according to claim 5, characterized in that: In the step 1, the length of the thread pasted at the grid circumferential center position (8) of the trailing edge (7) of the flow blade of the cascade block (6) along the flow direction of the cascade block (6) should not exceed the blade spacing, that is, the distance between the corresponding points of two adjacent flow blades along the frontal line direction.

7. A visual quantitative measurement method for the airflow angle at the outlet of the thrust reverser blade cascade according to claim 6, characterized in that: In step 3: before the test, a clear cascade image is captured by increasing the exposure time. 1 , I 2 , to I 1 , I 2 Perform image processing and obtain the image coordinates of the three corner points at the grid positions (m,n), (m+1,n), and (m,n+1) by extracting the corner points and and Based on the triangulation method, the spatial three-dimensional coordinates P of these three corner points in the camera coordinate system are obtained. m,n , P m+1,n and P m,n+1 , where P m,n and P m+1,n Circumferentially adjacent, P m,n and P m,n+1 Flow to adjacent areas; Calculate the axis vector of the coordinate system of the current grid: The coordinate system vector matrix of the grid of the blade block (6) is obtained as follows:

8. A visual quantitative measurement method for the airflow angle at the outlet of the thrust reverser blade cascade according to claim 7, characterized in that: In step 5: based on the Steger line center detection algorithm, the two camera images of the wire in the system are obtained respectively. The line center image coordinates l 1 and l 2 After matching the thread targets with the same name according to the corresponding constraints, the image coordinates of the two end points of the thread in the grid (m,n) are extracted. and The spatial three-dimensional coordinates L of the two end points of the silk thread in the camera coordinate system are obtained based on triangulation reconstruction. mn,1 and L mn,2 , where L mn,1 is the end point of the thread, L mn,2 It is the free end point of the wire.

9. A visual quantitative measurement method for the airflow angle at the outlet of a thrust reverser cascade according to claim 8, characterized in that: In the steps: the three-dimensional coordinates of the endpoints of the thread in the camera coordinate system are rotated by the rotation relationship R mn Convert to the grid coordinate system to get the new thread endpoint coordinate E mn,1 =L mn,1 / R mn and E mn,2 =L mn,2 / R mn , then in the grid coordinate system, the thread vector under the action of airflow during the test is That is, the outlet airflow angle represented by the silk line at the current position is obtained; The angle between the projection of this vector on the grid yoz plane and the y-axis: The angle between the projection of this vector on the grid xoy plane and the x-axis:

Images